Bacteriophages of pneumococcus (Streptococcus pneumoniae) are being examined with the primary objective of adding genetic tools to complement transformation by cellular DNA, also studied in this laboratory. Results to date have led to characterizing infection by both mature phage DNA and replicating intermediate extracted from infected cells. New results show that RNA and RNase strongly affect the transfection process, and the mechanism of this is being studied. A phage-associated gene transfer process that has many but not all of the properties of generalized transduction has also been found, and its study continues. Recombination among phage mutants adds a third new system for pneumococcus genetics. These processes are all being examined in cell strains carrying one or more mutations in properties relevant to recombination and repair processes. In addition, unusual bases in two phage DNAs have been found and are being studied.